Nonsinging reamplifying circuits



Jan. 3l, 1928.

A TTORNE Y lili Patented Jan., 31, 1928,

unirse stares 1,657,462 PATENT OFFICE.

LLOYI ESPENSUHIED, OF HOLLIS, NEW YORK, ASSIGNOR 'IO AMERICAN TELEPHONE ND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

NONSING'ING REAMPLIFYING CIRCUITS.

Application led May 15,

rllhis invention relates to signaling circuits and more particularly to arrangements for amplifying weak signaling currents.

In accordance with the present invention it is proposed to treat the .energy to be amplified by passing it Iagain and again through an amplifier successively at different frequencies so that the energy is amplified a plurality of times by a single amplifier. Between each transmissionthrough the amplifier the energy is shifted in frequency in some well known manner, as for example, by modulating it with a carrier frequency. The method is peculiarly adapted to signaling systems such as radio receiving circuits or other forms of carrier circuits in which the signaling energy is received at a high frequency and is translated to an ordinary signaling frequency. `Where the rv ceiving frequency is quite high it is often desirable to translate it to the low frequency signal by a succession of steps of demodulation and in accordance with the present invention the stepped-down frequency may be passed through the same amplifier each time it is stepped-down. lWhile the invention, as stated, is peculiarly adapted to receiving apparatus of a radio or otherl carrier system it may be applied to the sending station of such a system with some economy, especially where the ordinary signaling frequency is stepped-up to a radio frequency by a plurality of steps of modulation.

One of the principal advantages of the method of the present invention resides in the possibility of working the amplifier up to its full capacity. An amplier may be capable of amplifying the input energy iinpressed upon it a given number of times independently of the amount of input energy impressed upon it.. If, however, the amplifler is used only to amplify a very Weak current and actually capable of amplifying an equal number of times a much larger current, it is at once apparent that a method by which the full working capacity of the amplifier may be utilized will be advantageous. Heretofore. it has been proposed to amplify very Weak signaling energy by passing it through a number of successions of amplifying devices until the output energy is great enough for the practical purposes of receiving or transmitting, as the case may be. In such a system only the last amplifier of the series, if any, will be opern ieee. serial no. 639,169.

ating at its full capacity. In accordance with the present invention, the entire process of several stages of amplification inay be accomplished with a single amplifier. The only instance in which it has been proposed to use the saine amplifier for successive ame plifications has been where a radio signal is passed through an amplifier at the receiving station, then detected, and the detected signal passed through the same amplifier. This method is limited, however, to tWo steps of aniplilication through the Same amplifier because the signal is translated from the radio frequency to the detected frequency in a single step. Where the received energy is initially very small it will be-obvious that such a method will not utilize the full working capacity of the amplifier and will not give a sufficiently strong signal, so that it will be necessary to pass the low frequency signal thus amplified through successive amplifiers until the desired energy amplification is attained.

The limit of the eiiiciency of the proposed method ofv amplification is, of course, the power carrying capacity of the amplifying tube circuit. Roughly, it may be stated'that the sum of the energy of all the vsuccessive frequencies combined must not exceed the carrying capacity of the tube. 0f course, if the tube is overloaded the currents of the several frequencies passing through it will be modulated together and interfering dis toi-ted components `Will be set up.,

The invention may now be more fully understood by reference to the following detailed description when read in connection with the accompanying drawing,the figure of which illustrates a preferred embodiment of the invention.

Referiing to the drawing, ML designates a receiving circuit over which modulated carrierY or radio frequencies, for example, may be received. In the4 case assumed, a iilter F, is provided in said circuit, said lter being designed to transmit a carrier-frequency of 1,000,000 cycles plus or minus a band of 2,000 cycles representing the voice signaling wave in accordance with which the carrier is modulated. This total band of 4,000 cycles is impressed upon a circuit 20 leading to an amplifier fi, of any well lrnown type such as, for example, a three-element vacuum tube amplifier. 'The received band, after being amplified by the amplifier A, ie

passed into an outgoing circuit 21, having a plurality of branches associated therewith. One of the branches includes a filter F1 for passing the same range of frequencies as the filter F, and beyond the filter a modulator Ml is provided. Thismodulator may be of the usual vacuum tube type`and is-so arranged that in addition to the amplified signalmg band of 1,000,000-cycles plus or minus 2,000 cycles impressed upon its input circuit there will be a local frequency of, say,

` 900,000 cycles impressed upon its input cir- 1' circuit 20 upon the amplifier A. The amplifier A again am lifies the .original received energy at a ifl'erent frequency and again passes it to the circuit 21.

A second branch of the circuit 21 is provided with a filter F2 which'selects the band of frequencies represented by 100,000 cycles of 100,000 cycles.

lband. The detected low frequency plus or minus 2,000 cycles and impresses said band upon a demodulator M2, which may also be of the well known vacuum tube type. In its output circuit there will appear a detected band of freo Cincies resulting from the interaction of the stepped-down carrier frequency of 100,000 cycles with the impressed frequency band extendinv over a range of 4,000 cycles in the neighborhood This detected band of frequencies will comprise a band from zero to 2,000 cycles, the original signal which modulated the carrier being within this band just referred to passes into an out omg circuit 23, leading from the modu ator M2 through a filter F, to the common input circuit 20, so that the detected band is im'- pressed upon the amplifier A and the recelved energy again amplified at still another frequency. The amplied energy of from zero to 2,000 cycles asses into the out oing circuit 21 which 1s provided with a ranch including a lter F3 which selects from the circuit 21 the final low frequency energy and transmits it to the final receiving circuit L.

It will be obvious that additional steps of amplification, by means of the sin le amplifier shown, ma be obtained by increasing the number of e uency translating steps to which the receive energy is subjected. In other words, each time an additional step of modulation is providedv the output energy the energy received is very weak and is quite high in frequency, they additional tubes used for modulating purposes will have to be provided in any event for the purpose of stepping the frequency down from its high frequency carrier form to its ordinary signalin frequency, so that where this is necessary t e method involves a clear gain in that a single amplifier may do the work of several and, in fact, may do all of the work of which a single amplifier is capable.

The input and output transformers of the amplifier A may be assumed to be any type of arrangement capable of transmitting a wide range of frequencies. Owing to the difficulty of designing transformers capable of efficient transmission over a wide range, it will be understood that the windings conventionally indicated in the drawing may represent, in actual practice, a multiple transformer arrangement of 'which the component units are each etlicient over a particular frequency range narrower than that over which the whole transformer operates.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departin from the spirit of the invention as defin in the appended claims.

What is claimed is:

1. An amplifying system comprising an amplifier, an incomin circuit and an outgoing circuit, a plura ity of feed-back connections between said incoming and outgoin circuits, means in each of said feed-bac connections for producing a change in the frequency of energy transmitted thereover which is different from that of each of the other connections, and means in each of said feed-back connections for selecting a given frequency from the outgoing circuit and im pressing a different frequency upon the incoming circuit.

2. An amplifying system comprising an amplifier, an incoming circuit and an out going circuit, a plura ity of feed-back connections between said incoming and outgoing circuits, means in each of said feed-back connections for producing a change in the frequency of energy transmitted thereover which is different from that of each of the other connections, and wave filters in each ill) of said feed-back connections for selecting a given frequency from the outgoing circuit and impressing a different frequency upon the incoming circuit.

3. An amplifying system comprising an amplifier, an incoming and an outgoing circuit, means to impress high frequency signais of small energy upon said incoming circuitfa feed-back connection from said outgoing circuit to said incoming circuit, means in said feed-hack connection to step down lthe amplified energy to an intermediate frequency stage, means in said feed-back connection to impress the intermediate freuency energy upon said amplifier for furt er amplification, a second feed-back connection from said outgoing circuit to said incoming circuit, means in said second feedhack connection to further 'step down the freuency after the second stage of amplification to a third frequency, and means to impress the re-stepped-down energy upon the incoming circuit of said amplifier.

4. An amplifying system comprising an amplifier, an incoming circuit and an outgoing circuit, means to impress high fre` quency signals of small energy upon said incoming circuit of said amplifier, a feedback connection from said outgoing circuit to said incoming circuit, means in said feedhack circuit to beat the amplified high frequency signal energy with energy of another frequency to produce a signal Wave of lower frequency than the original signal wave,

means to impress the lower signal wave upon said incomin circuit for further amplification, a secon feed-back connection from the outgoing circuit to the incoming circuit, means in said second feed-back connection for stepping down said lower frequency quency signals of small energy upon said v amplifier after amplification, a feed-back connection from said outgoing circuit to said incoming circuit, means in said feed-hack connection to step down the amplified -energy to an intermediate frequency stage, a filter in said feed-hack connection for selecting the intermediate frequency energy and impressing it upon said amplifier for further amplification, a second feed-back connection from said outgoing circuit to said incoming circuit, means in' said second feed-back connection to Vfurther'step down the frequency after the second stage of amplification to a third frequency, and a filter in said second feed-back connection to select said third freuency and impress it upon said amplifier 'or further amplification.

In testimony whereof, I have signed my name to this specification this 14th day of May 1923.

LLOYD ESPENSCHED. 

